It is the conventional practice in high speed automatic press operations to feed a strip of stock material from a coil to a die of a press for stamping or the like at a preselected length of the stock material. The stock material must be fed from the coil in timed relation with the press operation by a press feed having feed rolls or grippers. Once in the press, the stock material is moved into registration with the die by pilots as the feed means are momentarily released from engagement with the stock material. The stock material is then held in position in the die for the press operation. After the press operation is completed the feed means are actuated to advance another preselected length of the stock material to the press. Therefore, the feeding of the stock material to the press must be coordinated with each press operation so that during each press cycle a new preselected length of stock material is in position in the die of the press.
U.S. Pat. Nos. 4,133,216 and 4,138,913 disclose one type of press feed where the feed length is changed by changing gears in the drive train between a cam drive and the feed rolls. Such a geared cam press feed is driven in synchronization with a press through an input shaft, typical from the crankshaft of the press, and converts the rotation of the input shaft to a noncontinuous stepwise, intermittent rotational movement of an output shaft that drives the feel rolls through a drive train. The feed rolls advance intermittently in segments through a rotational cycle preferably with dwell periods between the advances. During dwell periods, the feed rolls are not rotated and the stamping operation is performed in the die in the press. The feed rolls clamp the stock material at all times except during positioning of pilots during the press cycle.
U.S. Pat. Nos. 3,758,011 and 3,784,075 describe another type of press feed where the feed length is changed by a pivoted lever mechanism positioned in the drive train between a cardan drive and the feed rolls. The cardan drive is driven through an input shaft in synchronization with a press, and converts the continuous rotation of the input shaft into oscillating movement of a lever. One end of the lever is driven by the oscillating movement by the cardan drive and the other end of the lever is coupled to and drives the feed rolls. The feed length can be changed by moving the pivot of the lever along the length of the lever during each press cycle, when the feed rolls are released and returned, and a separate brake mechanism stops the stock material during roll return. See also, Japanese Patent Application Serial No. 53-43284, where a cam drive is used instead of the cardan drive, the pivot of the lever is fixed, and the connection of coupling from the end of the lever to the feed rolls is moved along the lever to change feed length. Piloting is typically accomplished by a feed roll release driven by a cam driven by the input shaft to the cardan drive. Adjustment of the piloting position in the press cycle is accomplished normally by rotationally positioning the cam relative to the input shaft.
U.S. Pat. No. 4,316,569 discloses another type of press feed where the feed length is changed by an adjustable cam drive. The cam drive is driven through an input shaft in synchronization with a press, and converts the continuous rotation movement of the input shaft into an intermittent, oscillating movement of an output shaft. An output shaft is fixed to one end portion of the output shaft of the cam drive, and a link mechanism is connected between the output shaft and the feed rolls. To change the feed length, the distance is changed between the output shaft from the cam drive and the connection of the link mechanism to the output shaft, preferably by connecting the link mechanism to a slide moved along the output shaft with a threaded adjusting means. The feed rolls clamp the stock material during forward advance of the feed length in the press and die, and a roll release releases the feed roll during the return in each press cycle and a clamp mechanism clamps the stock material during roll return. Both the roll release and the clamp mechanism are usually driven by separate cams driven by the input shaft to the cam drive. Piloting is accomplished by a adjustment between the cams actuating the roll release and material clamp, or by providing a third cam also driven by the input shaft that momentarily releases the material clamp. Adjustment of the piloting position in the press cycle is again accomplished manually by rotationally positioning the third cam relative to the input shaft.
One of the problems in all types of press feed such as those described above is positively driving both feed rolls efficiently and effectively with substantially uniform pressure. One press feed with such dual driven feed rolls is described in U.S. Pat. No. 4,601,420. One end of the link mechanism adjacent to the feed rolls is attached to an elongated orthogonal slider block which is slideably received in a horizontally extending guide groove provided in a guide channel secured to the feed housing. The slider block has a second block (or blocks) having vertically extending guide groove extending at right angles to the horizontally extending guide grooves. A first swing member is mounted in at one end to a first feed roll shaft and is drivingly connected at its other end to a slide positioned in the vertically extending guide groove, and a second swing member mounted at one end to a second feed roll shaft and drivingly connected at its other end to a slide positioned in the groove in the vertically extending groove. As the link mechanism oscillates, the orthoganal slider block also oscillates along the horizontally extending groove. Concurrently, the slides in the vertically extending grooves oscillate because of the oscillating motion of slider block to effect oscillating movement of the feed rolls.
The press feed of U.S. Pat. No. 4,601,420 experiences problems because the orthogonal slider block must be constrained to travel only in a path along the horizontal guide groove, and also the substantial area of surface contact between the orthogonal slider block the horizontal groove. The horizontal groove and the slider block must be machined to close fitting tolerances to achieve high speed press feeding. Friction and heat between the orthogonal slider block and the horizontally extending guide groove can cause degradation of lubricants, and to maintenance and replacement of worn parts and resulting costly downtime of the press feed and press. If, on the other hand, clearance between the slider block and the horizontal groove is provided to reduce friction, misalignment and related feed inaccuracies increase. Moreover, the orthagonal slider block has inertia that must be overcome at high speed operation (e.g., 1500-2000 spm) of the press feed and press, and presents a limiting factor to high speed operation.
A need exists, therefore, for a press feed positively driving both feed rolls in synchronization simply and efficiently, with substantially uniform press to the stock material by both feed rolls.